1. Field of the Invention
The present invention relates to light beacons and, more specifically, to light beacons for mounting on the apex of tall obstructions which present a hazard to air traffic.
2. Description of the Related Art
Light beacons for marking navigational hazards have been known and used for some time. Light beacons used to mark and identify tall obstructions which may present hazards to air traffic are required to meet certain specifications as developed by the Federal Aviation Administration and as spelled out in FAA Advisory Circular 150/5345-43. These specifications require that such light beacons be capable of generating a 360.degree. light beam in a horizontal plane while also meeting peak photometric light intensity and beam spread dimensions for both the vertical and horizontal planes.
To the inventors' knowledge, all qualified suppliers of light beacons meeting the above-mentioned FAA specification utilize either a 250 mm or 300 mm acrylic Fresnel lens cover with either a vertically or horizontally mounted helical flash lamp. Such known beacons are typically powered by an electrical power supply located at the base of the tall structure on which the beacon is mounted.
However, Fresnel lenses of the known light beacons are more efficiently used with a filament-type or point-type light source. With other types of light sources, such as a helical lamp, the efficiency of the Fresnel lens is reduced. Due to the FAA light output requirements for these types of beacons, the helical flash lamp must be made considerably larger in output than a point source type of light and results in reduced efficiency of the Fresnel lens. Furthermore, while the FAA requirements specify a vertical beam pattern having a 3.degree. arc minimum, it specifies that the lower edge of the vertical beam spread must lie between 1.5.degree. and 0.5.degree. below the horizontal. In order to meet this requirement the known beacon obstruction lights position the helical lamp within the lens cover in a position which lowers the efficient use of the output illumination.
Furthermore, the beacon obstruction lights utilizing a Fresnel lens cover are not easily adapted to vary the intensity or spread of the beam generated so as to accommodate varying land contours where the obstruction might be situated. Also, such known obstruction beacon lights produce a simple beam pattern and are not easily adapted to produce composite beam patterns for particular applications.
Still further, the helical flash lamps in these known beacons are typically mounted on one end to stand upright and therefore require a relatively large Fresnel lens cover. Obviously, a larger lens cover results in increased wind loading when the beacon is mounted on the obstruction and is more expensive to manufacture than would be smaller covers.